[CrazyIvan888]

So, I have a misfire in Cylinder #4, and the oil gets black VERY quickly after an oil change. So I'm guessing this points to bad piston rings allowing blow-by of combustion gases into the crankcase.
The misfire seems to go away around 2200 RPM.

Anyway, my question is, can I safely unplug the #4 injector to stop fuel being fed to that cylinder? Or will it trigger mad problems?

1999 Forester, Auto, 164,xxx miles.

Thanks!
Ivan

 

[Blue Fox]

Why would you want to remove the injector? Are you planning on running the engine for a while in the as-is condition. If so, I would leave it plugged in. It might be missing, but it's still working (just not 100%). If you unplug the injector, it won't be working at all.......it'll run on 3 cylinders, and it'll be pretty much unusable (believe me, I ran on 3 cylinders before, it's horrific). If your oil is getting dirty faster, and you think piston rings is the cause, then your motor is already in need of a rebuild, so I wouldn't worry about the oil getting dirty at this point.

What I would do ASAP is go down to Harbor Freight, buy a cheap compression-check tool, and check your compression in that cylinder to see if your problem really is compression/piston rings. Either that or take your car to a trusted shop and have them perform a compression check AND a leak-down test on the car. It'll set you back $100-150, but you'll get a definite answer to what is/isn't wrong.

 

[CrazyIvan888]

Correct, I'm thinking I'm going to be running as-is for a while. Used SOHC engines seem to be scarce.

I'll do a compression check to verify, but the previous owner stated that Cylinder #4 was "losing compression" and I just did an ignition tune-up and verified spark, so I'm pretty sure it's a compression issue.

If I end up doing a rebuild, can I remove the cylinder block with the engine in-car?

Thanks,
CI888

 

[craigbhp]

Try a can of engine restorer it may stop the mis-fires. I have had it work on a cylinder with 25% leakage past the rings.

 

[CrazyIvan888]

Yep, got a V8-sized can in there right now!

Oh, and another question: Will running a higher-octane (premium) fuel help to remedy the mis-fires?

 

[craigbhp]

I would not think the fuel will make a difference. Did the engine restorer make a difference? If not I would have a leak down test down on cylinder number 4 it may need a valve job. Did you check the valve clearance yet?

 

[CrazyIvan888]

The Restore hasn't made a noticeable difference yet, it's been in there for a couple hundred miles. Haven't touched the valves. Is it fairly straightforward, or something a shop should do?

 

[craigbhp]

The restore will work in a few miles of driving. The valve adjustment is not hard. Take the 5 bolts out of the valve cover and remove it. Then take the left hand timing cover off 3 bolts. Look for a arrow on the left cam sprocket 12:00 is number 1 cylinder 3:00 is 3 6:00 is 2 9:00 is 4 if I remember right

 

[CrazyIvan888]

Ok, sounds easy. Just looked up the valve clearances, looks like the intake valve is supposed to be at .2mm and the exhaust valve at .25mm. Gotta see if I can find my feeler gauge now.

Will update with the results! Thanks for all the help so far!

 

[CrazyIvan888]

Just got done with the valve adjustment, started her up and the misfire is still there.

Intake valves are on the top, exhaust valves on the bottom, correct?
The valves were a bit too tight on Cylinder #4, but if adjusting them fixed the problem, then it should be evident immediately, right?

 

[BAC5.2]

When did you last change the plugs?

Unplug the plug wire for #4 (from the spark plug and the coil pack) and swap it with the wire from #2. If the misfire follows the wires, replace the spark plug wires.

If that doesn't work, swap the plugs from cylinder 4 to cylinder 3 (and vice versa). If the misfire doesn't change, check the coil pack on top of the intake manifold. As you go up in miles, it's common for those to fail.

That's the first thing I'd do.

 

[CrazyIvan888]

Plugs and wires are brand new, I checked the spark and it's good. So I'm pretty sure it's a problem with compression, but I don't know where to start looking next and don't want to dump a lot of money into this thing.

 

[BAC5.2]

Start with a compression test. The testers are only like $20.

 

[funkymonkey1002]

Is it leaking anything by the headgaskets? My friends dohc legacy blew the headgasket and was misfiring on that side.

 

[craigbhp]

I would have a leak down test done. If it just needs a valve job it is not a big deal the heads are easy to remove.

 

[BAC5.2]

I would have a leak down test done. If it just needs a valve job it is not a big deal the heads are easy to remove.

It only takes a few more minutes to pull a piston out once the heads are off.

 

[CrazyIvan888]

No leaks that I can see, did a compression test and it's extremely low, maybe 20 PSI.

By "valve job", you mean replace the valves? What all parts would I need? I'm assuming valves, head gasket, valve guides.
I'm sure there's other stuff, but it appears that no-one sells a kit for rebuilding valves, so I'm not sure what all I should replace and what can be re-used.

I checked my fuel mileage today when I filled her up with gas, and it came out to be about 24 MPG. That's a lot better than I expected with the misfire.

CI888

 

[craigbhp]

It only takes a few more minutes to pull a piston out once the heads are off.

Why would you pull the motor to remove the heads? I can remove both heads with the motor in the car in under an hour.

 

[craigbhp]

No leaks that I can see, did a compression test and it's extremely low, maybe 20 PSI.

By "valve job", you mean replace the valves? What all parts would I need? I'm assuming valves, head gasket, valve guides.
I'm sure there's other stuff, but it appears that no-one sells a kit for rebuilding valves, so I'm not sure what all I should replace and what can be re-used.

I checked my fuel mileage today when I filled her up with gas, and it came out to be about 24 MPG. That's a lot better than I expected with the misfire.

CI888

Well you need to have a leakage test performed. If the leakage is past the valves then you would need to remove the head and have a machine shop cut the valves and seats. If the leakage is by the piston rings you would be better off finding a used motor.

 

[CrazyIvan888]

I would love to find a used motor for a grand or maybe even less, but they seem awfully scarce. Most of the ones I see for sale online are the DOHC versions.